Transport of water and solutes across sheep visceral pleura.

The fluid and solute transport properties of pleural tissue were studied using specimens of intact visceral pleura from adult sheep lungs. After thoracotomy, a shallow incision through the pleural surface permitted 10-cm2 by 10-micrometer pieces of visceral pleura free of lung parenchyma to be peeled off the lung surface. The pleura was then mounted as a planar sheet separating 2 reservoirs of Krebs-Ringer solution. Electrical potential and resistance, hydraulic water permeability, and diffusional permeability to water and several hydrophilic solutes were measured. The results showed that (1) no spontaneous voltage difference was present across the pleura; (2) electrical resistance (27.1 omega/cm2) was very low; (3) hydraulic water permeability was extremely high (1.64 X 10(-8) ml/dyne-s); and (4) diffusional permeability was high, varying from 5.24 X 10(-4) cm/s for water to 4 X 10(-5) cm/s for hemoglobin. Blue dextran (molecular weight, 2 X 10(6) daltons) did not cross the pleura in measurable quantities. We concluded that the isolated visceral pleura of the adult sheep is an extremely "leaky" tissue that probably does not actively transport salt and water. These findings are consistent with a passive model of pleural fluid formation and reabsorption, and suggest that the transport properties of normal pleural tissue are unlikely to be responsible for any differences in composition between interstitial and pleural fluids.